Pub/Sub triggers

In Cloud Functions, a Pub/Sub trigger enables a function to be called in response to Pub/Sub messages. When you specify a Pub/Sub trigger for a function, you also specify a Pub/Sub topic. Your function will be called whenever a message is published to the specified topic.

For a function to use a Pub/Sub trigger, it must be implemented as an event-driven function:

The Google Events repository contains additional resources for working with event data.

Deployment

You can specify a Pub/Sub trigger when you deploy a function. See Deploy a Cloud Function for general instructions on how to deploy a function, and see this section for additional information specific to configuring Pub/Sub triggers during deployment.

gcloud

If you are deploying using the gcloud CLI, the flags shown here are used to configure Pub/Sub triggers:

gcloud functions deploy YOUR_FUNCTION_NAME \
--trigger-topic=YOUR_PUBSUB_TOPIC \
[--retry] \
...
  • The --trigger-topic flag specifies the Pub/Sub topic that the trigger will monitor. Messages published to this topic trigger calls to your function.
  • The --retry flag controls whether failed function calls are automatically retried. See Retrying event-driven functions for more information.

Legacy Pub/Sub events

Legacy functions in Cloud Functions (1st gen) use a different event type for Pub/Sub triggers:

gcloud functions deploy YOUR_FUNCTION_NAME \
--trigger-event=providers/cloud.pubsub/eventTypes/topic.publish \
--trigger-resource=YOUR_PUBSUB_TOPIC \
...

This event type is supported for legacy functions already consuming these events. However, we recommend using the --trigger-topic flag instead, as the legacy event type might be removed at a future date.

Console

If you are deploying using the Google Cloud console, you can configure a Pub/Sub trigger in the Trigger section.

  • For Cloud Functions (2nd gen):

    1. In the Trigger type field, choose Cloud Pub/Sub.
    2. In the Cloud Pub/Sub topic field, select a topic for the trigger to monitor. Messages published to this topic trigger calls to your function.
    3. Select or deselect the Retry on failure checkbox to control whether Cloud Functions automatically retries a failed function invocation. See Retrying event-driven functions for more information.
    4. Click More options to perform additional configuration on your trigger:

      • In the Trigger type field, specify one of Google sources, Custom, or Third-party:

        • Google sources lets you specify triggers for Pub/Sub, Cloud Storage, Firestore, and other Google event providers.In the Eventarc trigger pane, use the Event provider field to select the product that provides the type of event you want to trigger your function. Then in the Event field, select the event you want to use as a trigger.

        • The Custom option lets you produce and consume events from your application code. Follow the prompts in the Eventarc trigger pane to create a channel. A channel is a resource that is used as a pipeline to deliver custom events from producers to consumers. Custom events are published to a channel and an Eventarc trigger subscribes to those events.

        • The Third-party option let you integrate with non-Google providers that offer an Eventarc source. See third-party events in Eventarc for details.

      • In the Event field, select a triggering event. The default is google.cloud.pubsub.topic.v1.messagePublished.

      • Optionally, in the Service account field, select a service account to be used as the identity of the Eventarc trigger. See Trigger identity for more information.

    5. Click Save trigger.

  • For Cloud Functions (1st gen):

    1. In the Trigger type field, select Cloud Pub/Sub.
    2. In the Select a Cloud Pub/Sub topic field, select a topic for the trigger to monitor, or select Create a topic to open a window to create a new topic. When a message is published to your function's topic, that triggers a call to your function.
    3. Select or clear the Retry on failure checkbox to control whether failed function calls are automatically retried. See Retrying event-driven functions for more information.

Next steps